This invention relates generally to a steering apparatus for a motor vehicle and, more particularly, to a worm isolator assembly utilized in a damped worm assist mechanism for reducing audible noise in an electric power steering assist mechanism.
Presently, certain motor vehicles contain column-type power steering apparatus that employ an electric power steering assist mechanism. The electric power steering assist mechanism provides torque assist to the steering shaft of a vehicle via an electric motor and a worm/worm gear reduction mechanism. The worm/worm gear reduction mechanism is interposed between the output shaft and the motor to obtain an appropriate steering speed as well as sufficient steering assistance in the course of transmission of the rotational force from the motor to the output shaft.
When the motor vehicle is operating, clearances between the worm and worm gear teeth and between other adjacent components in the mechanism commonly result in xe2x80x9crattlexe2x80x9d noise. Road feedback forces and torques travel through the steering shaft to the worm gear. These vibration loads are transmitted through the worm gear to the worm. The oscillatory impact produced takes place where the worm and worm gear teeth mesh. This oscillatory impact translates into axial forces acting upon the worm. These axial forces react through the worm to the adjacent components and produce the resulting xe2x80x9crattlexe2x80x9d noise.
There exists a need for a worm/worm gear reduction mechanism with lower combined stiffness of the mechanical system and no free lash along the mechanism""s worm axis.
This invention offers further advantages and alternatives over the prior art by providing a gear isolator assembly that reduces audible noise in a gear reduction mechanism. According to the present invention, a gear isolator assembly is provided. The gear isolator assembly is preferably used in a gear reduction mechanism for reducing noise generated by a first gear meshing with a second gear during operation of the mechanism. In an exemplary embodiment, the first gear has a first axis of rotation about a first shaft and the second gear has a second axis of rotation about a second shaft. The first and second gears are rotatably mounted in a gearbox housing so that the first and second gears mesh with each other such that the first axis of the first gear is substantially perpendicular to the second axis of the second gear. The gear isolator assembly is preferably disposed within the gearbox housing about the second gear for reducing noise generated between the first and second gears during operation of the mechanism. More specifically, the first and second gears rotate about their respective axis during operation of the mechanism. It is this interaction between the first and second gears, which generates noise, which travels through the gearbox housing.
In an exemplary embodiment, the gear isolator assembly comprises an elastomeric member having first and second planar surfaces and inner and outer surfaces. Each of the inner and outer surfaces includes a plurality of ridges, which define a plurality of grooves there between. The elastomeric member is disposed between first and second washers. An exemplary washer has an annular planar section formed between opposing flared edges. First and second planar surfaces of the elastomeric member seat within the planar sections of the first and second washers between the respective flared edges. The design of the first and second planar surfaces of the elastomeric member permits the elastomeric member to compress under pressure.
Advantageously, the present invention may also provide a gear isolator assembly that can maintain a highly nonlinear spring rate over an extended distance of travel.
Advantageously, the present invention may also provide a gear isolator assembly that allows the first gear to float axially while controlling its axial movement.
Advantageously, the present invention may also provide a gear isolator assembly that can maintain an indefinite load at a positive stop height without a metal-to-metal interface, which contributes to a reduction of the audible noise of a gear reduction mechanism during operation.
Advantageously, the present invention may also provide a gear isolator assembly that can maintain an axial pre-load along the axis of the first gear and eliminate clearances between the components of a gear reduction mechanism, which contributes to a reduction of the audible noise of a gear reduction mechanism during operation.
Advantageously, the present invention may also provide a gear isolator assembly that produces a bearing preload, which delashes the gear reduction mechanism and contributes to a reduction of the audible noise of a gear reduction mechanism during operation.
The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.